Optimization of peritoneal fluid and leukocyte collection in patients with endometriosis

OBJECTIVE

To propose a standardized protocol for peritoneal free fluid and leukocyte sample collection in women with endometriosis suitable for biomedical research on the basis of the surgical procedure, the clinical and technical conditions, and the quality of the samples obtained.

DESIGN

Video showing the step-by-step collection procedure and the suitability of samples obtained for biomedical research.

SUBJECTS

This study included 103 women with confirmed endometriosis by pathology analysis, who signed informed consent and were recruited from the Hospital "Virgen de la Arrixaca", Murcia, Spain. The study was approved by the Ethics Committee of University of Murcia (CEI 3156/2020).

MAIN OUTCOME MEASURES

We analyzed the presence of free fluid in the peritoneal cavity and its relationship with hormonal treatment intake. In addition, the presence of blood contamination, the number of viable leukocytes and macrophages in free peritoneal fluid and lavages as well as their relationship with the lavage volume used, the body mass index, and the age of patients were analyzed.

RESULTS

The presence of free peritoneal fluid, in which cells and molecules could be quantified, was scarce in the patients (21%), and it was not significantly related to hormonal treatment intake. The cell viability was higher than 98% in all collected samples; although 54% showed good quality and enough cellularity to be used in biomedical research, 40% were contaminated with blood and 6% had low cellularity. The number of leukocytes and macrophages recovered from the peritoneal lavages correlated positively with the lavage volume used and negatively with the body mass index and was independent of the age of the patients.

CONCLUSION

We describe a standardized step-by-step procedure for peritoneal fluid and leukocyte collection in women with endometriosis, suitable for biomedical research, taking into account that not all women present free fluid in the peritoneal cavity. We propose to increase the lavage volume recommended by the World Endometriosis Research Foundation from 10 mL to at least 40 mL of sterile saline solution and its mobilization for at least 30 seconds within the peritoneal cavity, especially in patients with higher body mass index, to improve the efficiency of the procedure.

Potential of Sulforaphane and Broccoli Membrane Vesicles as Regulators of M1/M2 Human Macrophage Activity

Macrophages have emerged as important therapeutic targets in many human diseases. The aim of this study was to analyze the effect of broccoli membrane vesicles and sulphoraphane (SFN), either free or encapsulated, on the activity of human monocyte-derived M1 and M2 macrophage primary culture. Our results show that exposure for 24 h to SFN 25 µM, free and encapsulated, induced a potent reduction on the activity of human M1 and M2 macrophages, downregulating proinflammatory and anti-inflammatory cytokines and phagocytic capability on C. albicans. The broccoli membrane vesicles do not represent inert nanocarriers, as they have low amounts of bioactive compounds, being able to modulate the cytokine production, depending on the inflammatory state of the cells. They could induce opposite effects to that of higher doses of SFN, reflecting its hormetic effect. These data reinforce the potential use of broccoli compounds as therapeutic agents not only for inflammatory diseases, but they also open new clinical possibilities for applications in other diseases related to immunodeficiency, autoimmunity, or in cancer therapy. Considering the variability of their biological effects in different scenarios, a proper therapeutic strategy with Brassica bioactive compounds should be designed for each pathology.

Analysis of the anti-inflammatory potential of Brassica bioactive compounds in a human macrophage-like cell model derived from HL-60 cells

BACKGROUND

Chronic inflammatory diseases are major causes of global morbidity and mortality. Acute inflammation is meant to protect the body against foreign agents, but it also plays a major role in tissue repairment. Several mediators are involved in this process, including pro-inflammatory cytokines produced by macrophages. Occasionally, if the inflammatory response is not resolved, the acute inflammatory process can evolve into a chronic inflammation. Natural compounds from vegetables are considered as an important source of active agents with potential to treat or prevent inflammatory related pathologies and could be used as an alternative of the therapeutic agents currently in use, such as non-steroidal anti-inflammatory drugs (NSAIDs), which present several side effects.

METHODS

In this research work we evaluated in vitro the anti-inflammatory activity of a series of ten phytochemicals present in Brassica, measured as the potential of those compounds to reduce the production of key pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β) by a human macrophage-like cell model of HL-60 cells RESULTS: Most of the tested phytochemicals (including the most representative bioactive molecules of the major classes of compounds present in cruciferous foods such as glucosinolates, isothiocyanates, hydroxycinnamic acids, flavonols and anthocyanins) demonstrated significant anti-inflammatory activity at micromolar level in the absence of cytotoxic effects in this human macrophage-like cell model.

CONCLUSION

These data confirm that phytochemicals commonly obtained from Brassica may be potential therapeutic leads to treat or prevent human chronic inflammation and related diseases.

Recent insights into the characteristics and role of peritoneal macrophages from ascites of cirrhotic patients

Macrophages are a diverse myeloid cell population involved in innate and adaptive immune responses, embryonic development, wound repair, and regulation of tissue homeostasis. These cells link the innate and adaptive immunities and are crucial in the development and sustainment of various inflammatory diseases. Macrophages are tissue-resident cells in steady-state conditions; however, they are also recruited from blood monocytes after local pathogen invasion or tissue injury. Peritoneal macrophages vary based on their cell complexity, phenotype, and functional capabilities. These cells regulate inflammation and control bacterial infections in the ascites of decompensated cirrhotic patients. Our recent work reported several phenotypic and functional characteristics of these cells under both healthy and pathological conditions. A direct association between cell size, CD14/CD16 expression, intracellular level of GATA-6, and expression of CD206 and HLA-DR activation/maturation markers, indicate that the large peritoneal macrophage CD14^highCD16^high subset constitutes the mature phenotype of human resident peritoneal macrophages during homeostasis. Moreover, elevated expression of CD14/CD16 is related to the phagocytic capacity. The novel large CD14^highCD16^high peritoneal subpopulation is increased in the ascites of cirrhotic patients and is highly sensitive to lipopolysaccharide (LPS)-induced activation, thereby exhibiting features of inflammatory priming. Thus, phosphorylation of ERK1/2, PKB/Akt, and c-Jun is remarkably increased in response to LPS in vitro, whereas that of p38 MAPK is reduced compared with the monocyte-derived macrophages from the blood of healthy controls. Furthermore, in vitro activated monocyte-derived macrophages from ascites of cirrhotic patients secreted significantly higher levels of IL-6, IL-10, and TNF-α and lower amounts of IL-1β and IL-12 than the corresponding cells from healthy donor’s blood. Based on these results, other authors have recently reported that the surface expression level of CD206 can be used to identify mature, resident, inflammatory peritoneal macrophages in patients with cirrhosis. Soluble CD206 is released from activated large peritoneal macrophages, and increased concentrations in patients with cirrhosis and spontaneous bacterial peritonitis (SBP) indicate reduced odds of survival for 90 d. Hence, the level of soluble CD206 in ascites might be used to identify patients with SBP at risk of death. In conclusion, peritoneal macrophages present in ascites of cirrhotic patients display multiple phenotypic modifications characterized by reduced ratio of cells expressing several membrane markers, together with an increase in the ratios of complex and intermediate subpopulations and a decrease in the classic-like subset. These modifications may lead to the identification of novel pharmaceutical targets for prevention and treatment of hepatic damage.

The Role of Peritoneal Macrophages in Endometriosis

Endometriosis is an estrogen-dependent gynecological disorder, defined as the growth of endometrial stromal cells and glands at extrauterine sites. Endometriotic lesions are more frequently located into the abdominal cavity, although they can also be implanted in distant places. Among its etiological factors, the presence of immune dysregulation occupies a prominent place, pointing out the beneficial and harmful outcomes of macrophages in the pathogenesis of this disease. Macrophages are tissue-resident cells that connect innate and adaptive immunity, playing a key role in maintaining local homeostasis in healthy conditions and being critical in the development and sustainment of many inflammatory diseases. Macrophages accumulate in the peritoneal cavity of women with endometriosis, but their ability to clear migrated endometrial fragments seems to be inefficient. Hence, the characteristics of the peritoneal immune system in endometriosis must be further studied to facilitate the search for new diagnostic and therapeutic tools. In this review, we summarize recent relevant advances obtained in both mouse, as the main animal model used to study endometriosis, and human, focusing on peritoneal macrophages obtained from endometriotic patients and healthy donors, under the perspective of its future clinical translation to the role that these cells play on this pathology.

Hypothetical roadmap towards endometriosis: prenatal endocrine-disrupting chemical pollutant exposure, anogenital distance, gut-genital microbiota and subclinical infections

BACKGROUND

Endometriosis is a gynaecological hormone-dependent disorder that is defined by histological lesions generated by the growth of endometrial-like tissue out of the uterus cavity, most commonly engrafted within the peritoneal cavity, although these lesions can also be located in distant organs. Endometriosis affects ~10% of women of reproductive age, frequently producing severe and, sometimes, incapacitating symptoms, including chronic pelvic pain, dysmenorrhea and dyspareunia, among others. Furthermore, endometriosis causes infertility in ~30% of affected women. Despite intense research on the mechanisms involved in the initial development and later progression of endometriosis, many questions remain unanswered and its aetiology remains unknown. Recent studies have demonstrated the critical role played by the relationship between the microbiome and mucosal immunology in preventing sexually transmitted diseases (HIV), infertility and several gynaecologic diseases.

OBJECTIVE AND RATIONALE

In this review, we sought to respond to the main research question related to the aetiology of endometriosis. We provide a model pointing out several risk factors that could explain the development of endometriosis. The hypothesis arises from bringing together current findings from large distinct areas, linking high prenatal exposure to environmental endocrine-disrupting chemicals with a short anogenital distance, female genital tract contamination with the faecal microbiota and the active role of genital subclinical microbial infections in the development and clinical progression of endometriosis.

SEARCH METHODS

We performed a search of the scientific literature published until 2019 in the PubMed database. The search strategy included the following keywords in various combinations: endometriosis, anogenital distance, chemical pollutants, endocrine-disrupting chemicals, prenatal exposure to endocrine-disrupting chemicals, the microbiome of the female reproductive tract, microbiota and genital tract, bacterial vaginosis, endometritis, oestrogens and microbiota and microbiota-immune system interactions.

OUTCOMES

On searching the corresponding bibliography, we found frequent associations between environmental endocrine-disrupting chemicals and endometriosis risk. Likewise, recent evidence and hypotheses have suggested the active role of genital subclinical microbial infections in the development and clinical progression of endometriosis. Hence, we can envisage a direct relationship between higher prenatal exposure to oestrogens or estrogenic endocrine-disrupting compounds (phthalates, bisphenols, organochlorine pesticides and others) and a shorter anogenital distance, which could favour frequent postnatal episodes of faecal microbiota contamination of the vulva and vagina, producing cervicovaginal microbiota dysbiosis. This relationship would disrupt local antimicrobial defences, subverting the homeostasis state and inducing a subclinical inflammatory response that could evolve into a sustained immune dysregulation, closing the vicious cycle responsible for the development of endometriosis.

WIDER IMPLICATIONS

Determining the aetiology of endometriosis is a challenging issue. Posing a new hypothesis on this subject provides the initial tool necessary to design future experimental, clinical and epidemiological research that could allow for a better understanding of the origin of this disease. Furthermore, advances in the understanding of its aetiology would allow the identification of new therapeutics and preventive actions.

Isolation of functional mature peritoneal macrophages from healthy humans

Macrophages play an important role in the inflammatory response. Their various biological functions are induced by different membrane receptors, including Toll-like receptors, which trigger several intracellular signaling cascades and activate the inflammasomes, which in turn elicit the release of inflammatory mediators such as cytokines. In this study, we present a novel method for the isolation of human mature peritoneal macrophages. This method can be easily implemented by gynecologists who routinely perform laparoscopy for sterilization by tubal ligation or surgically intervene in benign gynecological pathologies. Our method confirms that macrophages are the main peritoneal leukocyte subpopulation isolated from the human peritoneum in homeostasis. We showed that primary human peritoneal macrophages present phagocytic and oxidative activities, and respond to activation of the main proinflammatory pathways such as Toll-like receptors and inflammasomes, resulting in the secretion of different proinflammatory cytokines. Therefore, this method provides a useful tool for characterizing primary human macrophages as control cells for studies of molecular inflammatory pathways in steady-state conditions and for comparing them with those obtained from pathologies involving the peritoneal cavity. Furthermore, it will facilitate advances in the screening of anti-inflammatory compounds in the human system.

Is TCR/pMHC Affinity a Good Estimate of the T-cell Response? An Answer Based on Predictions From 12 Phenotypic Models

On the T-cell surface the TCR is the only molecule that senses antigen, and the engagement of TCR with its specific antigenic peptide (agonist)/MHC complex (pMHC) is determined by the biochemical parameters of the TCR-pMHC interaction. This interaction is the keystone of the adaptive immune response by triggering intracellular signaling pathways that induce the expression of genes required for T cell-mediated effector functions, such as T cell proliferation, cytokine secretion and cytotoxicity. To study the TCR-pMHC interaction one of its properties most extensively analyzed has been TCR-pMHC affinity. However, and despite of intensive experimental research, the results obtained are far from conclusive. Here, to determine if TCR-pMHC affinity is a reliable parameter to characterize T-cell responses, a systematic study has been performed based on the predictions of 12 phenotypic models. This approach has the advantage that allow us to study the response of a given system as a function of only those parameters in which we are interested while other system parameters remain constant. A little surprising, only the simple occupancy model predicts a direct relationship between affinity and response so that an increase in affinity always leads to larger responses. Conversely, in the others more elaborate models this clear situation does not occur, i.e., that a general positive correlation between affinity and immune response does not exist. This is mainly because affinity values are given by the quotient k _on/k _off where k _on and k _off are the rate constants of the binding process (i.e., affinity is in fact the quotient of two parameters), so that different sets of these rate constants can give the same value of affinity. However, except in the occupancy model, the predicted T-cell responses depend on the individual values of k _on and k _off rather than on their quotient k _on/k _off. This allows: a) that systems with the same affinity can show quite different responses; and b) that systems with low affinity may exhibit larger responses than systems with higher affinities. This would make affinity a poor estimate of T-cell responses and, as a result, data correlations between affinity and immune response should be interpreted and used with caution.

Anti-leukemia activity of 4-amino-2-aryl-6,9-dichlorobenzo[g]pteridines

Pteridines are bicyclic heterocyclic compounds with a pyrazino[2,3-d]pyrimidine nucleus that have shown a wide range of therapeutic utilities. Concretely, 4-aminopteridine derivatives have demonstrated both anti-inflammatory and anti-cancer properties, and some of them, such as methotrexate, are profusely used in medical practice. We have recently synthesized and tested the biological activity of a novel series of 4-amino-2-aryl-6,9-dichlorobenzo[g]pteridines, finding that they present anti-inflammatory properties, as they were able to inhibit in vitro the production of pro-inflammatory cytokines TNF-α and IL-6. Now, we have evaluated the anti-tumor potential of these compounds on HL-60 and K562 leukemia cell lines. Cells growing at exponential rate were exposed to decreasing doses of each compound, from 50 to 0.39 μM, for 24, 48, and 72 h. Cell viability was tested by MTT assay and cell death fashion determined by annexin V/propidium iodide assay. The cytotoxicity of the compounds was determined in differentiated macrophage-like HL-60 cells and in human peripheral blood mononuclear cells to evaluate the potential side effects on quiescent tumor cells and normal cells, respectively. Among the series, compounds 1a, 1b, 1g, 1j, and 1k showed anti-proliferative activity. Compounds 1j and 1k were active against both HL-60 and K562 cells, with a lower IC₅₀ against HL-60 cells. Compounds 1a, 1b, and 1g had a great cytotoxic activity against HL-60, but they were far less potent against K562 cells. None had side effects in differentiated tumor cells or in human peripheral blood mononuclear cells. In conclusion, our results demonstrate that some compounds of this series of 4-amino-2-aryl-6,9-dichlorobenzo[g]pteridines have anti-cancer properties in vitro.

Therapeutic potential of pteridine derivatives: A comprehensive review

Pteridines are aromatic compounds formed by fused pyrazine and pyrimidine rings. Many living organisms synthesize pteridines, where they act as pigments, enzymatic cofactors, or immune system activation molecules. This variety of biological functions has motivated the synthesis of a huge number of pteridine derivatives with the aim of studying their therapeutic potential. This review gathers the state-of-the-art of pteridine derivatives, describing their biological activities and molecular targets. The antitumor activity of pteridine-based compounds is one of the most studied and advanced therapeutic potentials, for which several molecular targets have been identified. Nevertheless, pteridines are also considered as very promising therapeutics for the treatment of chronic inflammation-related diseases. On the other hand, many pteridine derivatives have been tested for antimicrobial activities but, although some of them resulted to be active in preliminary assays, a deeper research is needed in this area. Moreover, pteridines may be of use in the treatment of many other diseases, such as diabetes, osteoporosis, ischemia, or neurodegeneration, among others. Thus, the diversity of the biological activities shown by these compounds highlights the promising therapeutic use of pteridine derivatives. Indeed, methotrexate, pralatrexate, and triamterene are Food and Drug Administration approved pteridines, while many others are currently under study in clinical trials.

Intracellular signaling modifications involved in the anti-inflammatory effect of 4-alkoxy-6,9-dichloro[1,2,4]triazolo[4,3-a]quinoxalines on macrophages

Inflammation is part of a complex biological response directed by the immune system to fight pathogens and maintain homeostasis. Dysregulation of the inflammatory process leads to development of chronic inflammatory or autoimmune diseases. Several cell types, such as macrophages, and cytokines such as interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) are involved in the regulation of inflammation. The important role played by these cytokines as mediators of the inflammatory process and the side effects of current therapies have promoted the search of new therapeutic alternatives. Quinoxalines are important compounds allowing a wide range of chemical modifications in order to provide an extensive repertoire of biological activities. We have previously shown that a series of 4-alkoxy-6,9-dichloro[1,2,4]triazolo[4,3-a]quinoxalines exhibit potent anti-inflammatory activity, inhibiting the production of TNF-α and IL-6. Our aim here was to study the mechanism thereby this series of compounds act upon different intracellular signaling pathways to uncover their potential molecular targets. By using immunoblotting assays, we found that these compounds inhibit ERK 1/2 and JNK/c-Jun cascades, and reduce c-Fos expression, while activate the anti-inflammatory PI3K/Akt route. These results provide further information on their effect upon the intracellular signal transduction mechanisms leading to inhibition of TNF-α and IL-6 secretion. Our results may be of great interest for the pharmaceutical industry, and could be used as a starting point for the development of new and more potent anti-inflammatory drugs derived from the quinoxaline core.

Attenuated JNK signaling in multidrug-resistant leukemic cells. Dual role of MAPK in cell survival

Having found previously that leukemic cells with multidrug resistant (MDR) phenotype, but not their sensitive counterparts, exhibit collateral sensitivity to cold stress in a P-gp-dependent manner, our aim was to study the signaling pathways involved in this phenomenon in sensitive (L1210) and resistant cells (L1210R and CBMC-6). It was observed that the acquisition of MDR phenotype by leukemic cells or their transfection with the extrussion pump, P-gp, modifies the activation profile and regulation of Mitogen-Activated Protein Kinases (MAPK) in cells exposed to low temperatures. More specifically, cold stress provoked the activation of c-Jun N-terminal kinase (JNK) in sensitive cells, while attenuated JNK signaling was observed in MDR cells. This effect was also observed, although with less intensity, in P-gp-transfected cells. Using pharmacological inhibitors to determine the role of MAPK in leukemic cell survival in physiological conditions or under cold stress, a dual temperature-dependent role was observed for JNK in MDR cell survival. At 37°C JNK is necessary for the survival of parental, resistant and P-gp-transfected cells; however, the use of inhibitors of either extracellular signal-regulated protein kinase (ERK) or JNK significantly counteracts cold-induced death of resistant and P-gp-transfected cells, supporting a role for ERK and JNK in cold-stress induced cell death. Finally, a connectivity model concerning MAPK is proposed, summarizing how cold stress and MDR-1 might trigger apoptosis in resistant cell lines. These findings on MDR cells may assist in the design of specific therapeutic strategies to complement current chemotherapy.

TCR/pMHC Interaction: Phenotypic Model for an Unsolved Enigma

TCR-pMHC interaction is the keystone of the adaptive immune response. This process exhibits an impressive capacity of speed, sensitivity, and discrimination that allows detecting foreign pMHCs at very low concentration among much more abundant self-pMHC ligands. However, and despite over three decades of intensive research, the mechanisms by which this remarkable discrimination and sensitivity is attained remain controversial. In kinetic proofreading mechanisms (KPR), an increase of specificity occurs by reducing the sensitivity. To overcome this difficulty, more elaborate models including feedback processes or induced rebinding have been incorporated into the KPR scheme. Here a new approach based on the assumption that the proofreading chain behaves differently for foreign- and self-pMHC complexes has been integrated into a phenotypic model in which the complexes responsible for T cell activation stabilize (for foreign peptides) or weaken (for foreign peptides), resulting in a dramatic increase in sensitivity and specificity. Stabilization and destabilization of complexes may be caused by conformational changes, rebinding, or any other process leading to variations in the dissociation rate constants of the complexes transmitting the activation. The numerical solution and the analytical expression for the steady-state response as a function of k_off(i) (i = 0, 1, …, N, where C₀, C₁, …, C_N are the complexes in the proofreading chain) are provided. The activation chain speeds up, and larger increases in sensitivity and discrimination are obtained if the rate of activation along the proofreading chain increases for foreign pMHCs and decreases for self-ligands. Experimental implications and comparison with current models are discussed.

Quinoxalines Potential to Target Pathologies

The study of quinoxalines has increased immeasurably during the last two decades, due firstly to their relatively simple chemical synthesis, which has generated a vast variety of compounds with diverse structural modifications, and secondly, to the wide therapeutic potential and biological activities exhibited by this family of compounds. Quinoxalines constitute a rising biomedical class of low-molecular weight heterocyclic compounds with potential functions as antitumour, anti-inflammatory, antibacterial, antiviral, antifungal, antiparasitic and antidiabetic agents, as well as being of interest for the potential treatment of glaucoma, insomnia, cardiovascular and neurological diseases, among others. However, a deeper knowledge of the molecular targets of quinoxalines that fulfil a key role in certain pathologies is required for the development of new and more specific drugs through a rational design strategy to avoid undesirable side effects. In the present review, we summarize the most important molecular targets of the quinoxaline derivatives discovered to date, thus providing a first reference index for researchers to identify the potential targets of their quinoxalines derived collections, which could facilitate the development of new quinoxaline- based therapies.

Regulatory role of PI3K-protein kinase B on the release of interleukin-1β in peritoneal macrophages from the ascites of cirrhotic patients

Great effort has been paid to identify novel targets for pharmaceutical intervention to control inflammation associated with different diseases. We have studied the effect of signalling inhibitors in the secretion of the proinflammatory and profibrogenic cytokine interleukin (IL)-1β in monocyte-derived macrophages (M-DM) obtained from the ascites of cirrhotic patients and compared with those obtained from the blood of healthy donors. Peritoneal M-DM were isolated from non-infected ascites of cirrhotic patients and stimulated in vitro with lipopolysaccharide (LPS) and heat-killed Candida albicans in the presence or absence of inhibitors for c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase kinase 1 (MEK1), p38 mitogen-activated protein kinase (MAPK) and phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K). The IL1B and CASP1 gene expression were evaluated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The expression of IL-1β and caspase-1 were determined by Western blot. IL-1β was also assayed by enzyme-linked immunosorbent assay (ELISA) in cell culture supernatants. Results revealed that MEK1 and JNK inhibition significantly reduced the basal and stimulated IL-1β secretion, while the p38 MAPK inhibitor had no effect on IL-1β levels. On the contrary, inhibition of PI3K increased the secretion of IL-1β from stimulated M-DM. The activating effect of PI3K inhibitor on IL-1β release was mediated mainly by the enhancement of the intracellular IL-1β and caspase-1 content release to the extracellular medium and not by increasing the corresponding mRNA and protein expression levels. These data point towards the role of MEK1 and JNK inhibitors, in contrast to the PI3K-protein kinase B inhibitors, as potential therapeutic tools for pharmaceutical intervention to diminish hepatic damage by reducing the inflammatory response mediated by IL-1β associated with liver failure.

Collateral sensitivity to cold stress and differential BCL-2 family expression in new daunomycin-resistant lymphoblastoid cell lines

The acquisition of a multidrug-resistant (MDR) phenotype by tumor cells is one of the main causes of chemotherapy failure in cancer, and, usually, is due to the increased expression of P-glycoprotein (MDR-1, P-gp, ABCB1), a pump that expels chemotherapeutics from the cell and/or regulates apoptosis. Thus, it is fundamental to find drugs or stress stimuli with a capacity to induce apoptosis in such cells and to identify the mechanisms involved. We address this matter in human cells and establish new daunomycin (DNM)-resistant cell lines (IM-9R) by exposing the parental lymphoblastic cells (IM-9) to increasing doses of the anti-neoplastic drug, daunomycin. The resistance level of IM-9R cell lines, MDR-1 expression and functionality, collateral sensitivity and Bcl-2 and caspases protein expression are analyzed. As a result, we show for the first time that, unlike the parental cells, human lymphoblastic resistant cells exhibit collateral sensitivity to cold stress, confirming that this phenomenon is not exclusive to murine leukemic cells, but a broader one associated with the acquisition of drug resistance. Furthermore, the new resistant cell lines undergo a significant increase in active caspase-3 and -9 levels and drastic changes in Bcl-2 family protein expression during the process of MDR phenotype acquisition.

MHC-I molecules selectively inhibit cell-mediated cytotoxicity triggered by ITAM-coupled activating receptors and 2B4

NK cell effector functions are controlled by a combination of inhibitory receptors, which modulate NK cell activation initiated by stimulatory receptors. Most of the canonical NK cell inhibitory receptors recognize allelic forms of classical and non-classical MHC class I molecules. Furthermore, high expression of MHC-I molecules on effector immune cells is also associated with reverse signaling, giving rise to several immune-regulatory functions. Consequently, the inhibitory function of MHC class I expressed on a human NKL cell line and activated primary NK and T cells on different activating receptors are analyzed in this paper. Our results reveal that MHC-I molecules display specific patterns of “selective” inhibition over cytotoxicity and cytokine production induced by ITAM-dependent receptors and 2B4, but not on NKG2D. This contrasts with the best known “canonical” inhibitory receptors, which constitutively inhibit both functions, regardless of the activating receptor involved. Our results support the existence of a new fine-tuner inhibitory function for MHC-I molecules expressed on cytotoxic effector cells that could be involved in establishing self-tolerance in mature activated NK cells, and could also be important in tumor and infected cell recognition.

Mathematical modelling and computational study of two-dimensional and three-dimensional dynamics of receptor-ligand interactions in signalling response mechanisms

Cell signalling processes involve receptor trafficking through highly connected networks of interacting components. The binding of surface receptors to their specific ligands is a key factor for the control and triggering of signalling pathways. But the binding process still presents many enigmas and, by analogy with surface catalytic reactions, two different mechanisms can be conceived: the first mechanism is related to the Eley-Rideal (ER) mechanism, i.e. the bulk-dissolved ligand interacts directly by pure three-dimensional (3D) diffusion with the specific surface receptor; the second mechanism is similar to the Langmuir-Hinshelwood (LH) process, i.e. 3D diffusion of the ligand to the cell surface followed by reversible ligand adsorption and subsequent two-dimensional (2D) surface diffusion to the receptor. A situation where both mechanisms simultaneously contribute to the signalling process could also occur. The aim of this paper is to perform a computational study of the behavior of the signalling response when these different mechanisms for ligand-receptor interactions are integrated into a model for signal transduction and ligand transport. To this end, partial differential equations have been used to develop spatio-temporal models that show trafficking dynamics of ligands, cell surface components, and intracellular signalling molecules through the different domains of the system. The mathematical modeling developed for these mechanisms has been applied to the study of two situations frequently found in cell systems: (a) dependence of the signal response on cell density; and (b) enhancement of the signalling response in a synaptic environment.

Role of MAP kinases and PI3K-Akt on the cytokine inflammatory profile of peritoneal macrophages from the ascites of cirrhotic patients

AIMS

Several new approaches targeting inflammation associated with different diseases are in clinical development.

OBJECTIVE

To explore the role played by MAPK and PI3K-Akt pathways on the release of cytokines in monocyte-derived macrophages (M-DM) obtained from the ascites of cirrhotic patients to identify novel targets for pharmaceutical intervention to prevent hepatic damage.

METHODS

M-DM were isolated from the ascites of cirrhotic patients and stimulated in vitro with LPS and heat-killed Candida albicans in the presence or absence of the inhibitors for MEK1, p38 MAPK, JNK and PI3K. The MAPK phosphorylation levels were determined by Western Blot. Cell culture supernatants were assayed by ELISA for TNF-α, IL-6 and IL-10.

RESULTS

The release of the pro-inflammatory cytokines IL-6 and TNF-α at baseline was more effectively reduced by the MAPK inhibitors, while the basal IL-10 anti-inflammatory cytokine secretion was only and strongly (90.3%) affected by the PI3K inhibitor. The incubation of peritoneal M-DM in the presence of LPS and C. albicans increased the release of IL-6, TNF-α and IL-10. LPS-induced pro-inflammatory cytokines secretion was more sensitive to MAPK inhibitors, whereas that induced by C. albicans was more susceptible to inhibition of PI3K. Finally, inhibition of PI3K almost completely suppressed the secretion of IL-10 in stimulated M-DM.

CONCLUSIONS

These results demonstrate that pro-inflammatory cytokines release in M-DM from this clinical setting strongly depends on the MAPK signalling pathways, differs depending on the microbial stimulus added and confirms the prominent role of the PI3K-Akt pathway in the modulation of IL-10-mediated anti-inflammatory function.

Acquisition of MDR phenotype by leukemic cells is associated with increased caspase-3 activity and a collateral sensitivity to cold stress

The acquisition of a multidrug-resistant (MDR) phenotype by tumor cells that renders them unsusceptible to anti-neoplasic agents is one of the main causes of chemotherapy failure in human malignancies. The increased expression of P-glycoprotein (MDR1, P-gp, ABCB1) in tumor cells contributes to drug resistance by extruding chemotherapeutic agents or by regulating programmed cell death. In a study of MDR cell survival under cold stress conditions, it was found that resistant leukemic cells with P-gp over-expression, but not their sensitive counterparts, are hypersensitive to cold-induced cell death when exposed to temperatures below 4 °C. The transfection of parental cells with a P-gp-expressing plasmid makes these cells sensitive to cold stress, demonstrating an association between P-gp expression and cell death at low temperatures. Furthermore, we observed increased basal expression and activity of effector caspase-3 at physiological temperature (37 °C) in MDR cells compared with their parental cell line. Treatment with a caspase-3 inhibitor partially rescues MDR leukemic cells from cold-induced apoptosis, which suggests that the cell death mechanism may require caspase-3 activity. Taken together, these findings demonstrate that P-gp expression plays a role in MDR cell survival, and is accompanied by a collateral sensitivity to death induced by cold stress. These findings may assist in the design of specific therapeutic strategies to complement current chemotherapy treatment against cancer.

The peritoneal macrophage inflammatory profile in cirrhosis depends on the alcoholic or hepatitis C viral etiology and is related to ERK phosphorylation

BACKGROUND

The development of ascites in cirrhotic patients generally heralds a deterioration in their clinical status. A differential gene expression profile between alcohol- and hepatitis C virus (HCV)-related cirrhosis has been described from liver biopsies, especially those associated with innate immune responses. The aim of this work was to identify functional differences in the inflammatory profile of monocyte-derived macrophages from ascites in cirrhotic patients of different etiologies in an attempt to extrapolate studies from liver biopsies to immune cells in ascites. To this end 45 patients with cirrhosis and non-infected ascites, distributed according to disease etiology, HCV (n=15) or alcohol (n=30) were studied. Cytokines and the cell content in ascites were assessed by ELISA and flow cytometry, respectively. Cytokines and ERK phosphorylation in peritoneal monocyte-derived macrophages isolated and stimulated in vitro were also determined.

RESULTS

A different pattern of leukocyte migration to the peritoneal cavity and differences in the primed status of macrophages in cirrhosis were observed depending on the viral or alcoholic etiology. Whereas no differences in peripheral blood cell subpopulations could be observed, T lymphocyte, monocyte and polymorphonuclear cell populations in ascites were more abundant in the HCV than the alcohol etiology. HCV-related cirrhosis etiology was associated with a decreased inflammatory profile in ascites compared with the alcoholic etiology. Higher levels of IL-10 and lower levels of IL-6 and IL-12 were observed in ascitic fluid from the HCV group. Isolated peritoneal monocyte-derived macrophages maintained their primed status in vitro throughout the 24 h culture period. The level of ERK1/2 phosphorylation was higher in ALC peritoneal macrophages at baseline than in HCV patients, although the addition of LPS induced a greater increase in ERK1/2 phosphorylation in HCV than in ALC patients.

CONCLUSIONS

The macrophage inflammatory status is higher in ascites of alcohol-related cirrhotic patients than in HCV-related patients, which could be related with differences in bacterial translocation episodes or regulatory T cell populations. These findings should contribute to identifying potential prognostic and/or therapeutic targets for chronic liver diseases of different etiology.

Spatio-temporal dependence of the signaling response in immune-receptor trafficking networks regulated by cell density: a theoretical model

Cell signaling processes involve receptor trafficking through highly connected networks of interacting components. The binding of surface receptors to their specific ligands is a key factor for the control and triggering of signaling pathways. In most experimental systems, ligand concentration and cell density vary within a wide range of values. Dependence of the signal response on cell density is related with the extracellular volume available per cell. This dependence has previously been studied using non-spatial models which assume that signaling components are well mixed and uniformly distributed in a single compartment. In this paper, a mathematical model that shows the influence exerted by cell density on the spatio-temporal evolution of ligands, cell surface receptors, and intracellular signaling molecules is developed. To this end, partial differential equations were used to model ligand and receptor trafficking dynamics through the different domains of the whole system. This enabled us to analyze several interesting features involved with these systems, namely: a) how the perturbation caused by the signaling response propagates through the system; b) receptor internalization dynamics and how cell density affects the robustness of dose-response curves upon variation of the binding affinity; and c) that enhanced correlations between ligand input and system response are obtained under conditions that result in larger perturbations of the equilibrium . Finally, the results are compared with those obtained by considering that the above components are well mixed in a single compartment.

Epitope mapping, expression and post-translational modifications of two isoforms of CD33 (CD33M and CD33m) on lymphoid and myeloid human cells

We have tested the usefulness of several commercial anti-CD33 monoclonal antibodies (mAb) to determine the expression and localization of the two CD33 isoforms on several hematopoietic cell lines. The expression of the isoform CD33m, a CD33 transmembrane splice variant lacking the ligand-binding V immunoglobulin (Ig)-like domain, was detected by RT-polymerase chain reaction, western blot, confocal microscopy and flow cytometry on the membrane of several human cell types. CD33m was only detected by the anti-CD33 mAb HIM3-4 on the cell surface, whereas WM53, P67.6, 4D3, HIM3-4, WM54, D3HL60.251 or MY9 detected the CD33M isoform, indicating that HIM3-4 is the only mAb recognizing CD33 C(2) Ig domain. Accordingly, HIM3-4 binding to CD33 did not interfere with the binding of other antibodies against the CD33 V-domain. P67.6 mAb interfered with recognition by the rest of antibodies specific for the V domain. HIM3-4 staining could be increased after the sialidase treatment of all CD33(+) cells. However, this increase was stronger in activated T cells, suggesting a CD33 masking state in this cell population. Confocal microscopy analysis of CD33m HEK 293T-transfected cells revealed that this protein is expressed on the cell membrane and also detected in the Golgi compartment. CD33 is constitutively located outside the lipid raft domains, whereas cross-linked CD33 is highly recruited to this signaling platform. The unique ability of HIM3-4 mAb to detect the masking state of CD33 on different cell lineages makes it a good tool to improve the knowledge of the biological role of this sialic acid-binding Ig-like lectin.

Peritoneal macrophage priming in cirrhosis is related to ERK phosphorylation and IL-6 secretion

BACKGROUND

Bacterial infections are common complications arising in patients with cirrhosis and ascites. Translocation of bacterial DNA is a dynamic process that is associated with an increased inflammatory response and a poor prognosis in this setting. The aim of this study was to study whether peritoneal macrophages remain in a chronic primed status to allow a rapid response to subsequent events of bacterial translocation.

PATIENTS AND METHODS

Peritoneal monocyte-derived macrophages were isolated from 25 patients with cirrhosis and non-infected ascites and compared with donor's blood monocytes. Activation cell-surface markers were screened using flow-cytometry, and the phosphorylation state of ERK 1/2, p38 MAP Kinase, PKB/Akt and transcription factors c-Jun and p65 NFκB were evaluated using Western blot. Synthesis of tumour necrosis factor alpha, interleukin 6 (IL-6) and interleukin-10 (IL-10) at baseline and in response to bacterial stimuli was evaluated using ELISA.

RESULTS

A high expression of CD54, CD86 and HLA-DR at baseline was displayed by peritoneal macrophages. Increased phosphorylated levels of ERK1/2, protein kinase B (PKB) and c-Jun, together with IL-6 production, were observed in peritoneal macrophages at baseline compared with donors' blood monocytes. A positive correlation was established between basal IL-6 levels and extracellular signal-regulated kinase (ERK) phosphorylation in peritoneal macrophages from patients with cirrhosis (r=0·9; P=0·005). Addition of lipopolysaccharide induced higher phosphorylation levels of all studied signalling intermediates than synthetic-oligodeoxydinucleotides, but similar end-stage p65 NFκB.

CONCLUSIONS

A sustained immune response is present in ascitic fluid of cirrhotic patients, even in the temporal absence of bacterial antigens. This would facilitate a fast response, probably controlled by IL-6, against repeated bacterial-DNA translocation or in liver chronic inflammation.

Synthetic oligodeoxynucleotides induce MAP kinases activation in murine TIB-73 hepatocytes

AIMS

In this work we aimed to investigate the expression of TLR9 protein in the murine hepatocyte cell line TIB-73, compared to macrophage-like J774 cells, by Western blot analysis, and the role played by ERK 1/2 MAP kinase in the intracellular signals triggered by stimulation with CpG and non-CpG phosphodiester-ODN, and their more stable phosphorothioate-modified analogues.

RESULTS

TIB-73 hepatocytes express TLR9 protein. CpG and non-CpG ODN stimulation activated ERK 1/2 MAPK signal pathway in both hepatocytes and J774 murine macrophages. As expected, their phosphorothioate-CpG and non-CpG ODN analogues induced higher levels of ERK1/2 phosphorylation in TIB-73 cells, even higher than that induced in J774 cells under the same conditions. Phosphorylation of ERK 1/2 induced by synthetic ODN is dose-response dependent, being maximal at 100 microg/ml. Pretreatment of hepatocytes with an inhibitor of MEK-1 abrogated phosphorylation of ERK1/2 kinase.

CONCLUSIONS

TIB-73 hepatocytes constitutively express TLR9 and respond to synthetic ODN stimulation through a high ERK1/2 phosphorylation independent of CpG motifs. Slight differences were found on ERK1/2 activation when using phosphorothioate versus phosphodiester oligonucleotides.

Norfloxacin modulates the inflammatory response and directly affects neutrophils in patients with decompensated cirrhosis

BACKGROUND & AIMS

Patients with cirrhosis undergoing selective intestinal decontamination with norfloxacin show a reduction in serum cytokine levels, probably because of a combined effect of norfloxacin on bowel flora and neutrophils.

METHODS

Thirty-one patients with cirrhosis receiving norfloxacin (400 mg/day) were included. Blood samples were collected at 0.5-4 hours (peak samples group, n = 47) and at 22-24 hours (trough samples group, n = 84) after dose. Fifty-nine ascitic fluid samples were obtained. Single doses of norfloxacin and trimethoprim/sulfamethoxazole were administered to 13 and 5 patients, respectively, (temporal profile group) and samples were collected at 0, 0.5, 1, 1.5, 2, 4, and 24 hours. Norfloxacin, trimethoprim/sulfamethoxazole, cytokines, nitric oxide, expression levels of nuclear factor (NF)-kappaB and inhibitor of NF-kappaB (IkB-alpha), neutrophil oxidative burst, and rate of apoptotic events were determined.

RESULTS

All samples were bacterial DNA negative and had no significant levels of lipopolysaccharide. Serum and ascitic levels of tumor necrosis factor-alpha, interferon-gamma, interleukin-12, and nitric oxide were significantly lower in peak than in trough samples. A correlation was present between serum norfloxacins concentrations and tumor necrosis factor-alpha (r = -0.68; P < .001), interferon-gamma (r = -0.66; P < .001), interleukin-12 (r = -0.66; P < .001), and nitric oxide (r = -0.68; P < .001). Serum norfloxacin's highest concentrations (1 +/- 0.5 microg/mL) were achieved at 1-2 hours and concurred in time with the lower levels of cytokines and nitric oxide. Intracellular norfloxacin's highest levels (2 +/- 1 microg/mL/10(7) cells) were observed at 2 hours and concurred with a lower NF-kappaB expression, a reduced anion superoxide generation, and apoptotic rate in response to phorbol myristate acetate. Trimethoprim/sulfamethoxazole did not significantly modulate cytokine expression.

CONCLUSIONS

Norfloxacin but not trimethoprim/sulfamethoxazole modulates inflammatory response and directly affects neutrophils in patients with cirrhosis.

Role of trehalose-6P phosphatase (TPS2) in stress tolerance and resistance to macrophage killing in Candida albicans

Disruption of the TPS2 gene encoding the only trehalose-6P phosphatase activity in Candida albicans caused a pleiotropic defective phenotype, maintaining the cell wall integrity and the ability to form chlamydospores. A homozygous tps2Delta/tps2Delta showed reduced growth at high temperatures and a marked sensitivity to heat shock (42 degrees C) and severe oxidative exposure (50mM H(2)O(2)). Reintroduction of the TPS2 gene reversed these alterations. A more detailed study of the antioxidant response showed that exponential tps2Delta null cells displayed an adaptive response to oxidative stress as well as cross-tolerance between temperature and oxidative stress. Differential measurement of trehalose and trehalose-6P, using reliable new HPLC methodology, revealed a significant accumulation of trehalose-6P in tps2Delta cells, which was enhanced after oxidative exposure. In contrast, the level of trehalose-6P in parental cells was virtually undetectable, and oxidative treatment only induced the synthesis of free trehalose. A transitory increase in the expression of TPS2 and TPS1 genes was promoted in wild-type cells in response to acute (50mM) but not gentle (5mM) oxidative exposure. TPS1 and TPS2 oxidative-induced transcriptions were completely absent from the tps2Delta mutant. Exponential blastoconidia from both parental and tps2Delta/tps2Delta strains were completely phagocytosed by murine and human macrophages, triggering a subsequent proinflammatory response manifested by the release of TNF-alpha. Reflecting the lower resistance to oxidative stress displayed by the tps2Delta mutant, intracellular survival in resting and IFN-gamma and LPS-stimulated macrophages was also diminished. Taken together, our results confirm the mainly protective role played by the trehalose biosynthetic pathway in the cellular response to oxidative stress and subsequently in the resistance to phagocytosis in C. albicans, a defensive mechanism in which TPS2 would be involved.

Role of trehalose in resistance to macrophage killing: study with a tps1/tps1 trehalose-deficient mutant of Candida albicans

Accumulation of trehalose by yeast is an important protective mechanism against different stress conditions. This study examined the effect of trehalose on several growth features, as well as its association with the intracellular survival of yeasts exposed to macrophages. A tps1/tps1 mutant and its parental counterpart, CAI4, exhibited similar growth rates and preserved their dimorphic conversion and agglutination ability. However, electron-microscopy of cell-wall architecture showed a partial loss of material from the outer cell-wall layer in the tps1/tps1 mutant. Flow-cytometry revealed that the mutant had lower auto-fluorescence levels and a higher fluorescein isothiocynate staining efficiency. When co-cultured with macrophages, a slight reduction in binding to macrophages and slower ingestion kinetics were revealed for the tps1/tps1 mutant, but these did not interfere significantly with the amount of yeast ingested by macrophages after co-incubation for 2 h. Under the same conditions, CAI4 cells were more resistant to macrophage killing than was the tps1 null mutant, provided that the macrophages had been stimulated previously with interferon-gamma. Measurement of trehalose content and the anti-oxidant activities of yeast cells recovered after phagocytosis revealed that the trehalose content and the glutathione reductase activity were increased only in CAI4 cells, whereas levels of catalase activity were increased similarly in both strains. These results suggest that the presence of trehalose in Candida albicans is a contributory factor that protects the cell from injury caused by macrophages.

A study of CD33 (SIGLEC-3) antigen expression and function on activated human T and NK cells: two isoforms of CD33 are generated by alternative splicing

The expression of CD33, a restricted leukocyte antigen considered specific for myeloid lineage, has been studied extensively on lymphoid cells. We demonstrated that wide subsets of mitogen- or alloantigen-activated human T and natural killer (NK) cells express CD33 at protein and nucleic acid levels. CD33+ and CD33- T and NK cell populations showed identical surface expression of activation markers such as CD25, CD28, CD38, CD45RO, or CD95. Myeloid and lymphoid CD33 cDNA were identical. However, lymphoid CD33 protein had lower molecular weight, suggesting cell type-specific, post-translational modifications. Additionally, reverse transcriptase-polymerase chain reaction and Northern blot analysis showed an unknown CD33 isoform (CD33m) expressed on all CD33+ cell lines or T cell clones tested. CD33m was identical to CD33 (CD33M) in the signal peptide, the immunoglobulin (Ig) domain C2, the transmembrane, and the cytoplasmic regions but lacked the extracellular ligand-binding variable Ig-like domain encoded by the second exon. CD33m mRNA was mostly detected on NKL and myeloid cell lines but poorly expressed on B cell lines and T lymphocytes. The CD33m extracellular portion was successfully expressed as a soluble fusion protein on transfected human cells, suggesting a functional role on cell membranes. Cross-linking of CD33 diminished the cytotoxic activity of NKL cells against K562 and P815 target cells, working as an inhibitory receptor on NK cells. These data demonstrate that CD33 expression is not restricted to the myeloid lineage and could exist as two different splicing variants, which could play an important role in the regulation of human lymphoid and myeloid cells.

Implication of CpG-ODN and reactive oxygen species in the inhibition of intracellular growth of in hepatocytes

Bacterial DNA acts as an alert signal for eukaryotic cells through immunostimulatory CpG motifs. These sequences have therapeutic properties promoting protective immune TH1 responses and are recognized by a membrane protein belonging to the Toll-like receptor (TLR) family, named TLR-9. The aim of this study was to test the capability of murine hepatocytes to sense bacterial DNA and to develop antibacterial mechanisms against Salmonella typhimurium. We show that hepatocyte cell lines and mRNA extracts from murine liver constitutively express TLR-9, which is down-regulated by LPS and the mix of IFNgamma, IL-1beta and LPS. Also, we have found that hepatocyte cell lines can sense the presence of bacterial DNA and respond to it by increasing the pool of intracellular peroxides. This results in inhibition of intracellular growth of S. typhimurium when infected cells were incubated in the presence of CpG synthetic oligonucleotides (CpG-ODN). Expression of hepatocyte Mn-SOD is also induced by stimulation with CpG-oligodeoxynucleotides, LPS, and the mix of IFNgamma, IL-1beta and LPS. These results reinforce the prominent role of hepatocytes as a microbial product-responsive cell and the capabilities of CpG-ODN sequences as potent inducers of the innate immune response through the activation of a broad range of cell types.

Cross-linking of MHC class I molecules on human NK cells inhibits NK cell function, segregates MHC I from the NK cell synapse, and induces intracellular phosphotyrosines

Engagement of major histocompatibility complex (MHC) class I molecules on immune cells, where they are usually highly expressed, induces signal transduction events of unclear significance. We show here that antibody-mediated cross-linking of MHC-I molecules on human natural killer (NK) cells inhibits their cytotoxic activity against tumor target cells. Inhibition by anti-MHC class I monoclonal antibody exhibits molecular specificity and is an isotype and Fc-independent process. Physical hindrance of specific molecular recognition, induction of apoptosis, or reciprocal NK cell killing, which could be induced by cross-linking of MHC I molecules, has also been ruled out as putative mechanisms of inhibition. Confocal microscopy analysis revealed that MHC class I molecules on the surface of NK cells colocalize constitutively with GM1, a marker of lipid rafts. Cross-linking of MHC class I resulted in the asymmetric redistribution of GM1-enriched raft domains, which are concentrated to the immunological synapse, and MHC I molecules, which segregate to the opposite pole. Also, the cross-linking of MHC I on NK cells induced intracellular tyrosine phosphorylations. These results suggest that MHC I molecules on NK cells could transmit inhibitory signals upon engagement with putative ligands expressed on the surface of those cells that need to be protected from natural cytotoxicity.

Penetration of host cell lines by bacteria. Characteristics of the process of intracellular bacterial infection

A model which describes the characteristics of the penetration of the cells by bacteria is presented. Since the process of invasion is preceded necessarily by the step in which the bacteria adhere to the cells, the proposed model is based on the expressions previously derived for the process of adhesion, which allow us to determine the number of attached bacteria under different conditions. Thus, the model considers that invasion occurs irreversibly from attached bacteria to specific receptors located on the cell surface with a rate coefficient = ki so that the invasive capacity in a given bacterium-host cell system is mainly determined by the value of this coefficient. Once internalized, the bacteria can follow three different time courses, namely: 1) intracellular growth is hindered so that the bacteria remain in stationary phase, 2) there is a lag phase during which the bacteria stay in stationary phase before they are able to grow exponentially with a rate coefficient = kc, and 3) the bacteria exhibit a growth exponential phase as they enter the cells. In turn, the time course followed by extracellular bacteria also has a decisive influence on the process of invasion and, in this regard, unbound bacteria are considered either in stationary or in exponential phase. Expressions for these different situations have been derived, and from them, procedures to determine the levels of bacterial infection and for quantitative invasive data analysis are presented.